Sergio Aguero is expected to miss five to six weeks with knee surgery.
Aguero suffered the injury in Monday's win over Burnley.
Guardiola is confident Gabriel Jesus can replace Agüero, though Ilkay Gündogan, Raheem Sterling or Bernardo Silva will also be deployed at No 9 because of the regularity of matches.
Aguero has one more year at least at City, with his contract due to expire in summer 2021.
Jaime Jackson/The Guardian